1. Field of the Invention
The present invention generally relates to a light source module and applications thereof. More particularly, the present invention relates to a low cost light source module having a simple structure and superior light quality, and applications thereof.
2. Description of Related Art
A light source for illuminating an information source is often required in many applications. In particular, liquid crystal displays (LCDs) have become more and more popular in many electronic media. LCDs are commonly adopted in various applications, such as laptop computers, display monitors, video cameras, automatic teller machine displays, displays in avionics, televisions etc. In general, an illuminating apparatus (i.e., a backlight module) is required for the LCDs to illuminate the information to be displayed. A variety of light sources are used in an illuminating apparatus of an LCD, e.g., fluorescent lamps and light emitting diodes (LEDs). While the fluorescent lamps are inexpensive and require no complex control circuitry, they are sometimes inadequate for certain applications that require good color quality and prolonged lamp life time.
Accordingly, LEDs have been proposed for use as light sources, such as illuminating apparatuses for LCDs, for many reasons. The advantages of LED light sources include long life time, ease of replacement, robust mechanical property, and better color quality compared to fluorescent lamps. Certain applications (e.g., avionics) require a specific chromaticity of light emitted from the illuminating apparatus of LCD. However, most commercially available LEDs are made with a limited number of chromaticity choices and their chromaticity may change over time.
An LED light source with a raised LED 100, as shown in FIG. 1, to improve the chromaticity of a combined light was disclosed in U.S. Pat. No. 6,666,567. The raised LED 100 includes an LED diode 101 encased in a package 102 which is raised above the floor 103 of optical cavities. The raised structure permits light to be emitted from the base of the LED. Additionally, reflective protrusions may be placed beneath the raised LED to aid in redirecting the light trajectory. A combination of fluorescent lamps and LEDs were also proposed to form a hybrid light source.
As shown in FIG. 2 and FIG. 3, an LCD backlight 200, which includes a first LED array 201 that provides light with a first chromaticity and a second LED array 202 that provides light with a second chromaticity, was disclosed in another U.S. Pat. No. 6,608,614. The lights emitted from these two LED arrays 201 and 202 are combined through a combining element 301 (e.g., a wave guide) and then projected towards an LCD panel 302. The LED chip normally emits light in a direction which is approximately perpendicular to the chip surface. The directions of light emitted from the first and the second LED arrays are approximately perpendicular and parallel to the panel surface, respectively. A separate combining element 301 is required in this light source. The chromaticity of the combined light can only be adjusted by changing the chromaticity of the second LED array 202 through a control system (not shown).
According to another prior art, a Luxeon side-emitter having packaged LED chips was disclosed, as shown in FIG. 4. The side-emitter may provide good uniformity of combined light but the light intensity is poor. In addition, packaged LED chips normally occupy a large area.
It is known that the majority of lights emitted from LED chips travel in a direction approximately perpendicular to the chip surface. Therefore, the LED chips need to be arranged such that the lights emitted from different LED chips have a chance to be combined and mixed in order to achieve desired chromaticity before they reach a target. Accordingly, the present invention proposes using a less complex and low cost system to achieve high intensity and good color quality.